Portable memory devices, such as memory cards, are often used with consumer electronic devices, such as digital cameras, mobile phones, and personal computers (PCs), to store and/or transport data. In addition to a storage medium, many portable memory devices contain circuitry, such as a microprocessor or controller, that can transform logical addresses received from the host device to physical addresses used by the memory device, thereby allowing the circuitry on the memory device to control where data is stored in the storage medium.
Many memory devices use a rewritable memory, which allows a memory address to be erased and rewritten for system or user purposes. However, other memory devices use a one-time programmable (OTP) memory array. In an OTP memory array, once a memory cell at a memory address is changed to a programmed state, it cannot be changed back to its original, unprogrammed state. Because of this limitation on the number of times a memory address can be written, memory devices with OTP memory arrays may not be compatible with host devices that use the popular DOS FAT file system or other file systems that expect to be able to rewrite to a memory address. A similar problem occurs, to a lesser extent, with memory devices that use a few-time programmable (FTP) memory array, whose memory cells can be written more than once but not as many times as memory cells in a rewritable memory array.
Another type of memory device is a write-once, read-many (WORM) memory device. This memory device is not rewritable, so that data, once written, cannot be later changed, erased, or overwritten. This is useful for applications where data reliability and security are paramount, such as archival document storage or permanent record-keeping.